Page 62 - RCM - A practical Guide_V1

RCM - A Practical Guide

MSG-3. Further refinement of MSG-2, developed for the 757, 767 series aircraft and published in
October 1980 under the title, MSG-3: Airline/Manufacturer Maintenance Program Planning
Document.
Multiple failure. A failure event consisting of the sequential occurrence of two or more independent failures,
which may have consequences that would not be produced by any of the failures occurring
separately.
Non-significant Item. An item whose failure (or a hidden function whose part in a multiple failure) has no direct effect
on safety/environment or on the operational capability of the equipment, and involves no
exceptionally expensive failure modes.
On-condition (OC) task A scheduled task used to detect potential failures
Operational/economic The effect of a failure that does not have safety/environmental consequences, but which causes
consequences. a loss of mission essential equipment or results in high repair costs.

Potential failure. A quantifiable failure symptom that indicates that a functional failure is imminent.
Probability of survival. The probability that an item will survive to a specified operating age, under specified operation
conditions, without failure.
Reliability. The ability of an item to do a required function under stated conditions for a stated period of
time (BS 3811).
Reliability Centred A disciplined methodology used to determine the most cost effective maintenance tasks or
Maintenance (RCM). other actions necessary to realize the inherent reliability, optimum availability and safe
operation of an aircraft or equipment.
Safe fatigue life. A life limit imposed on an item that is subject to a critical failure. Established as some fraction of
the average age, or fatigue life, at which test data shows that failures will occur.
Safe life structure. Refer to MRP RA5720.
Safety/environment The consequence caused by a loss of a function or secondary damage resulting from a given
consequence. failure mode which produces a direct adverse effect on safety or the environment
Significant item (SI). A generic term for both Structurally Significant Items and Functionally Significant Items, which
are items whose failure has safety, environmental, operational or economic consequences. A
Significant Item may be classified as both a Structurally Significant Item and a Functionally
Significant Item.

Structural rating factors. Criteria based on fatigue, environmental damage, and accidental damage - used to rate
structurally significant items for the determination of examination frequencies.
Structurally Significant Item Refer to MRP RA 5720
(SSI).
Survival curve. A graph of the probability of survival of an item as a function of age, derived by actuarial analysis
of its service history. The area under the curve can be used to measure the average realized age
(expected life) of the item under consideration.

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